Zirconia (ZrO₂) Embedded in Carbon Nanowires via Electrospinning for Efficient Arsenic Removal from Water Combined with DFT Studies

To use zirconia (ZrO₂) as an efficient environmental adsorbent, it can be impregnated on a support to improve its physical properties and lower the overall cost. In this study, ZrO₂ embedded in carbon nanowires (ZCNs) is fabricated via an electrospinning method to remove arsenic (As) from water. The maximum adsorption capacity values of As­(III) and As­(V) on the ZCNs are 28.61 and 106.57 mg/g, respectively, at 40 °C. These capacities are considerably higher than those of pure ZrO₂ (2.56 and 3.65 mg/g for As­(III) and As­(V), respectively) created using the same procedure as for the ZCNs. Meanwhile, the adsorption behaviors of As­(III) and As­(V) on the ZCNs are endothermic and pH dependent and follow the Freundlich isotherm model and pseudo-first-order kinetic model. Both As­(III) and As­(V) are chemisorbed onto the ZCNs, which is confirmed by a partial density of state (PDOS) analysis and Dubinin–Radushkevich (D-R) model calculations. Furthermore, the ZCNs also possess the capability to enhance or catalyze the oxidation process of As­(III) to As­(V) using dissolved oxygen. This result is confirmed by a batch experiment, XPS analysis and Mulliken net charge analysis. Density functional theory (DFT) calculations indicate the different configurations of As­(III) and As­(V) complexes on the tetragonal ZrO₂ (t-ZrO₂)­(111) and monoclinic ZrO₂ (m-ZrO₂)­(111) planes, respectively. The adsorption energy (<i>E</i>_ad) of As­(V) is higher than that of As­(III) on both the t-ZrO₂(111) and m-ZrO₂ (111) planes (3.38 and 1.90 eV, respectively, for As­(V) and 0.37 and 0.12 eV, respectively, for As­(III))

Kinetics and Modeling of Degradation of Ionophore Antibiotics by UV and UV/H₂O₂

Ionophore antibiotics (IPAs), one of the major groups of pharmaceuticals used in livestock industry, have been found to contaminate agricultural runoff and surface waters via land application of animal manures as fertilizers. However, limited research has investigated the means to remove IPAs from water sources. This study investigates the degradation of IPAs by using ultraviolet (UV) photolysis and UV combined with hydrogen peroxide (UV/H₂O₂) advanced oxidation process (AOP) under low-pressure (LP) UV lamps in various water matrices. Three widely used (monensin, salinomycin, and narasin) and one model (nigericin) IPAs exhibit low light absorption in the UV range and degrade slowly at the light intensity of 3.36 × 10^–6 Einstein·L^–1·s^–1 under UV photolysis conditions. However, IPAs react with hydroxyl radicals produced by UV/H₂O₂ at fast reaction rates, with second-order reaction rate constants at (3.49–4.00) × 10⁹ M^–1·s^–1. Water matrix constituents enhanced the removal of IPAs by UV photolysis but inhibited UV/H₂O₂ process. A steady-state kinetic model successfully predicts the impact of water constituents on IPA degradation by UV/H₂O₂ and determines the optimal H₂O₂ dose by considering both energy consumption and IPA removal. LC/MS analysis of reaction products reveals the initial transformation pathways of IPAs via hydrogen atom abstraction and peroxidation during UV/H₂O₂. This study is among the first to provide a comprehensive understanding of the degradation of IPAs via UV/H₂O₂ AOP

Development of Linear Free Energy Relationships for Aqueous Phase Radical-Involved Chemical Reactions

Aqueous phase advanced oxidation processes (AOPs) produce hydroxyl radicals (HO•) which can completely oxidize electron rich organic compounds. The proper design and operation of AOPs require that we predict the formation and fate of the byproducts and their associated toxicity. Accordingly, there is a need to develop a first-principles kinetic model that can predict the dominant reaction pathways that potentially produce toxic byproducts. We have published some of our efforts on predicting the elementary reaction pathways and the HO• rate constants. Here we develop linear free energy relationships (LFERs) that predict the rate constants for aqueous phase radical reactions. The LFERs relate experimentally obtained kinetic rate constants to quantum mechanically calculated aqueous phase free energies of activation. The LFERs have been applied to 101 reactions, including (1) HO• addition to 15 aromatic compounds; (2) addition of molecular oxygen to 65 carbon-centered aliphatic and cyclohexadienyl radicals; (3) disproportionation of 10 peroxyl radicals, and (4) unimolecular decay of nine peroxyl radicals. The LFERs correlations predict the rate constants within a factor of 2 from the experimental values for HO• reactions and molecular oxygen addition, and a factor of 5 for peroxyl radical reactions. The LFERs and the elementary reaction pathways will enable us to predict the formation and initial fate of the byproducts in AOPs. Furthermore, our methodology can be applied to other environmental processes in which aqueous phase radical-involved reactions occur

Remediation of Petroleum-Contaminated Soil and Simultaneous Recovery of Oil by Fast Pyrolysis

Petroleum-contaminated soil (PCS) caused by the accidental release of crude oil into the environment, which occurs frequently during oil exploitation worldwide, needs efficient and cost-effective remediation. In this study, a fast pyrolysis technology was implemented to remediate the PCS and concurrently recover the oil. The remediation effect related to pyrolytic parameters, the recovery rate of oil and its possible formation pathway, and the physicochemical properties of the remediated PCS and its suitability for planting were systematically investigated. The results show that 50.9% carbon was recovered in oil, whose quality even exceeds that of crude oil. Both extractable total petroleum hydrocarbon (TPH) and water-soluble organic matter (SOM) in PCS were completely removed at 500 °C within 30 min. The remaining carbon in remediated PCS was determined to be in a stable and innocuous state, which has no adverse effect on wheat growth. On the basis of the systematically characterizations of initial PCS and pyrolytic products, a possible thermochemical mechanism was proposed which involves evaporation, cracking and polymerization. In addition, the energy consumption analysis and remediation effect of various PCSs indicate that fast pyrolysis is a viable and cost-effective method for PCS remediation

Weak-Bond-Based Photoreduction of Polybrominated Diphenyl Ethers on Graphene in Water

The photoreduction of polybrominated diphenyl ethers (PBDEs)a kind of persistent organic pollutants with high hydrophobicitywas achieved on graphene in aqueous solution. We first observed that reduced graphene oxide (RGO) exhibited higher reaction rate than graphene oxide (GO). FT-IR and elementary analysis indicated that GO first was reduced to RGO at the beginning of the irradiation, and RGO is the real photoactive species. The theoretical calculations and adsorption experiments reveal a new photochemical debromination pathway based on the weak interaction, such as hydrophobic interaction, π–π interaction, and halogen-binding interaction between the PBDEs and RGO. These interactions enable the photoinduced electron transfer from the RGO to PBDEs and lead to the efficient reductive debromination of PBDEs. This study provides a green and low-cost method for removal of the high hydrophobicity halogen organic pollutants in water with environmentally benign carbon nanomaterials

Acid-Catalyzed Transformation of Ionophore Veterinary Antibiotics: Reaction Mechanism and Product Implications

Ionophore antibiotics (IPAs) are polyether antimicrobials widely used in the livestock industry and may enter the environment via land application of animal waste and agricultural runoff. Information is scarce regarding potential transformation of IPAs under environmental conditions. This study is among the first to identify the propensity of IPAs to undergo acid-catalyzed transformation in mildly acidic aquatic systems and characterize the reactions in depth. The study focused on the most widely used monensin (MON) and salinomycin (SAL), and also included narasin (NAR) in the investigation. All three IPAs are susceptible to acid-catalyzed transformation. MON reacts much more slowly than SAL and NAR and exhibits a different kinetic behavior that is further evaluated by a reversible reaction kinetic model. Extensive product characterization identifies that the spiro-ketal group of IPAs is the reactive site for the acid-catalyzed hydrolytic transformation, yielding predominantly isomeric and other products. Toxicity evaluation of the transformation products shows that the products retain some antimicrobial properties. The occurrence of IPAs and isomeric transformation products is also observed in poultry litter and agricultural runoff samples. Considering the common presence of mildly acidic environments (pH 4–7) in soils and waters, the acid-catalyzed transformation identified in this study likely plays an important role in the environmental fate of IPAs

Responses of the Microalga <i>Chlorophyta</i> sp. to Bacterial Quorum Sensing Molecules (<i>N</i>‑Acylhomoserine Lactones): Aromatic Protein-Induced Self-Aggregation

Bacteria and microalgae often coexist during the recycling of microalgal bioresources in wastewater treatment processes. Although the bacteria may compete with the microalgae for nutrients, they could also facilitate microalgal harvesting by forming algal-bacterial aggregates. However, very little is known about interspecies interactions between bacteria and microalgae. In this study, we investigated the responses of a model microalga, <i>Chlorophyta</i> sp., to the typical quorum sensing (QS) molecules <i>N</i>-acylhomoserine lactones (AHLs) extracted from activated sludge bacteria. <i>Chlorophyta</i> sp. self-aggregated in 200 μm bioflocs by secreting 460–1000 kDa aromatic proteins upon interacting with AHLs, and the settling efficiency of <i>Chlorophyta</i> sp. reached as high as 41%. However, <i>Chlorophyta</i> sp. cells were essentially in a free suspension in the absence of AHLs. Fluorescence intensity of the aromatic proteins had significant (<i>P</i> < 0.05) relationship with the <i>Chlorophyta</i> sp. settleability, and showed a positive correlation, indicating that aromatic proteins helped aggregate microalga. Transcriptome results further revealed up-regulation of synthesis pathways for aromatic proteins from tyrosine and phenylalanine that was assisted by anthranilate accumulation. To the best of our knowledge, this is the first study to confirm that eukaryotic microorganisms can sense and respond to prokaryotic QS molecules

Preparation and Photoelectrochemical Performance of Visible-Light Active AgI/TiO₂‑NTs Composite with Rich β‑AgI

AgI sensitized TiO₂ nanotube arrays (AgI/TiO₂-NTs) with adjustable β/γ ratio of AgI were prepared by a simple dissolution–precipitation–calcination process. The samples were characterized by various techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, linear sweep voltammetry, electrochemical impedance spectroscopy, and Mott–Schottky plots. We found that calcination temperature (100–500 °C) had significant effect on regulating the phase of AgI. After calcination at 350 °C, the highest β/γ ratio of AgI was achieved. Moreover, greatly enhanced photocurrent response and reduced charge transfer resistance were also observed, which together led to easier generation and separation of photogenerated electron–hole pairs. Thus, for the reduction of Cr­(VI) under visible light, significantly enhanced photoelectrocatalytic (PEC) performance was observed using AgI/TiO₂-NTs calcined at 350 °C (denoted as AgI/TiO₂-NTs350) as photoanode and Ti foil as cathode, respectively. At very low content of AgI (1.25%), the estimated <i>k</i>_Cr(VI) (0.0155 min^–1) was nearly 5 times that of pure TiO₂-NTs350

Electrochemical Advanced Oxidation of Perfluorooctanoic Acid: Mechanisms and Process Optimization with Kinetic Modeling

Electrochemical advanced oxidation processes (EAOPs) are promising technologies for perfluorooctanoic acid (PFOA) degradation, but the mechanisms and preferred pathways for PFOA mineralization remain unknown. Herein, we proposed a plausible primary pathway for electrochemical PFOA mineralization using density functional theory (DFT) simulations and experiments. We neglected the unique effects of the anode surface and treated anodes as electron sinks only to acquire a general pathway. This was the essential first step toward fully revealing the primary pathway applicable to all anodes. Systematically exploring the roles of valence band holes (h+), hydroxyl radicals (HO•), and H2O, we found that h+, whose contribution was previously underestimated, dominated PFOA mineralization. Notably, the primary pathway did not generate short-chain perfluoroalkyl carboxylic acids (PFCAs), which were previously thought to be the main degradation intermediates, but generated other polyfluorinated alkyl substances (PFASs) that were rapidly degraded upon formation. Also, we developed a simplified kinetic model, which considered all of the main processes (mass transfer with electromigration included, surface adsorption/desorption, and oxidation on the anode surface), to simulate PFOA degradation in EAOPs. Our model can predict PFOA concentration profiles under various current densities, initial PFOA concentrations, and flow velocities

Impacts of Combined Cooling, Heating and Power Systems, and Rainwater Harvesting on Water Demand, Carbon Dioxide, and NO_<i>x</i> Emissions for Atlanta

The purpose of this study is to explore the potential water, CO₂ and NO_<i>x</i> emission, and cost savings that the deployment of decentralized water and energy technologies within two urban growth scenarios can achieve. We assess the effectiveness of urban growth, technological, and political strategies to reduce these burdens in the 13-county Atlanta metropolitan region. The urban growth between 2005 and 2030 was modeled for a business as usual (BAU) scenario and a more compact growth (MCG) scenario. We considered combined cooling, heating and power (CCHP) systems using microturbines for our decentralized energy technology and rooftop rainwater harvesting and low flow fixtures for the decentralized water technologies. Decentralized water and energy technologies had more of an impact in reducing the CO₂ and NO_<i>x</i> emissions and water withdrawal and consumption than an MCG growth scenario (which does not consider energy for transit). Decentralized energy can reduce the CO₂ and NO_<i>x</i> emissions by 8% and 63%, respectively. Decentralized energy and water technologies can reduce the water withdrawal and consumption in the MCG scenario by 49% and 50% respectively. Installing CCHP systems on both the existing and new building stocks with a net metering policy could reduce the CO₂, NO_<i>x</i>, and water consumption by 50%, 90%, and 75% respectively